Radio receiving system for microwaves



April 5, 1938. R. A. BRADEN 2,112,822

RADIO RECEIVING SYSTEM FOR MICROWAVES Filed NOV. 25, 1956 i Saga/www 3d I Bnventor 7l. ade,

Gttorneg Patented Apr. 5, 1938 PATENT OFFICE RADIO RECEIVING SYSTEM FOR MICRO- f WAVES Rene A. Braden, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application November 25, 1936, Serial No. 112,655

9 Claims.

This invention relates to a radio receiving system for microwave oscillations. More specifically, a magnetron detector and a magnetron oscillator are combined to form the first detector and local oscillator of a microwave superheterodyne receiver.

It is well known to those skilled in the art that electrodes of a irst detector and local oscillator may be arranged within a singlevacuum tube.

In general, such detector-oscillators operate as electron-coupled devices in which precautions are taken to shield the detector elements from the oscillator elements. The circuits associated with such detector-oscillators are comprised of concentrated inductors and capacitors which operate from ultra high frequencies to relatively low radio frequencies. If the difference in frequency between the incoming signal currents and the local oscillatory currents is slight, a small amount of coupling will cause the'currents to react on each other. This reaction is generally in the degenerative direction and causes increasing losses with increasing frequency. At ultra high frequencies the degenerative losses become excessive. If the reaction is in the regenerative direction, undesired oscillations are produced at the v higher frequencies. The present invention avoids these undesirable reactions in a microwave receiving system.

This invention has for its principal object an improved means for combining microwave incoming signal currents and local oscillatory currents.

Another object is to combine a pair of magnetron tubes and a single magnetic field, which is adjusted to afford a suitable operating characteristic for each magnetron.

Another object is to provide coupling means between the elements of a pair of magnetrons, Which will be substantially independent of the tunable lines connected to the magnetrons.

A further object is to combine the several ad- `iustments which are functions of the frequency characteristics of magnetrons.

This invention is illustrated by the accompanying schematic diagrams, in which Fig. 1 represents one embodiment of the invention,

Fig. 2 is a modification of the magnetron structure of Fig. 1; and

Fig. 3 is a further modification of the magnetron tube which may be used in the microwave receivers embodying this invention.y

Referring to Fig. l, an antenna I is connected to a transmission line 3, which may be tuned by the adjustable bridging member 5, The transtube (Cl. Z50-20) mission line 3 is terminated in anode electrodes 1 which, together with cathode 9, form a magnetron detector. The anodes 1 and cathode 9 are mounted within an evacuated envelope Il, which is positioned Within ,a magnetic field created by a solenoid I3, electromagnet, or other suitable means. The magnetic field is adjusted by a rheost-at I5, which controls the current flowing in the solenoid, ory other suitable means, such as a vacuum tube regulator.y

A second magnetron, comprising a pair of anodes I1 and a cathode I9, is preferably mounted within the envelope Il. The anodes of the two magnetrons are respectively positioned to provide a capacity coupling represented by dotted lines 2l. The anodes I1 of the second magnetron are connected to a transmission line 23, which is tuned by a bridging conductor 25. The anode current source 21 is connected to the anode electrodes of the first and second magnetrons by connecting potentiometers 29, 3l across the source 21 and leads 33,35 from the sliders of the potentiometers through choke coils 31, 39 to 4the midpoints of the bridging members 2,5, 5. The cathodes 3, I9 and the negative terminal of the anode source 21 are grounded to complete the circuits. Other means for regulating plate voltage may be used, such as vacuum tube regulators. The second magnetron generates oscillations of a frequency different from that of the received signals. Voltages generated by the second magnetron are impressed on the plates of the first magnetron by means of the capacity coupling 2l'.

Intermediate frequency currents, which are created by the difference frequency between incoming microwave currents and local oscillatory currents, are impressed upon a tuned `circuit 4I, which is included in the lead 35 between 'the bridging conductor 5 and potentiometer 3l; The tuned circuit 4I is coupled to an intermediate frequency amplifier 43 whose output circuit is connected to a second detector 45. The detector output is connected toa suitable amplifier or signal indicator not shown.

The operation of the foregoing circuit depends upon magnetronfope'rating characteristics and the characteristics of the resonant lines. The former characteristics are centimeters. 'Ihe resonant line characteristic may be expressed as where L=length in centimeters, nzintegral number of half-wave lengths and k=a fraction of a half-Wave length. Therefore, the magnetic field H varies as the voltage V as `and the resonant line L varies as A.

In order to operate the several adjustable units of the oscillator or of the detector with a single control, the potentiometers 29, 3| and the rheostat I5 are preferably arranged with a tapered Winding so that the voltage V will varyv as and the magnetic field will vary as While the bridge members 5, 25 are varied as the wave length A. The oscillator control and the detector control may be likewise combined. While the foregoing mathematical expressions indicate Athat a different magnetic field strength is required for optimum operation of the detector and oscillator, as a practical matter the frequency of the local oscillator may be a very small percent higher or lower than the incoming microwave. This difference frequency is so small that the optimum magnetic field may be selected for the oscillator, the detector, or at a frequency between these two. The magnetic field and resonant line adjustments are critical and may be combined only by observing the precautions set forthabove.

Fig. 2 shows a circuit diagram which is essentially the same as the circuit of Fig. 1. The difference is found in the magnetron tube structure. In the instant embodiment, four curved anode electrodes 5|, 53, 55, 51 are concentrically mounted around a cathode 59 and within an envelope 6|. Two of the anode electrodes 5| 55, together with the cathode 59 and magnetic field, form the elements of the magnetron connected to the local oscillator circuit. The remaining anodes 53, 51, together with the cathode 59 and magnetic field, form the magnetron detector elements. The tunable circuits and intermediate circuit are connected as previously described. (Anodes 53, 51 may be of the same radius or different radius from the anodes 5|, 55.)

In Fig. 3 the magnetron elements are arranged about a common cathode 60. One pair of split anodes 63, 65 are connected to one tunable transmission line and the other anodes 61, 69 are connected to ,the other transmission line. These elements are mounted Within a common evacuated envelope 1|, which is positioned within a magnetic field Whose lines of force are substantially parallel to the cathode 6|. 'Ihe magnetic field may be created by an electromagnet or solenoid. The spacing between the pairs of anode electrodes 63, 65 and B1, 69 is arranged to provide suitable coupling between oscillator and diQr elements as hereinbeefore described,

Thus the circuits and magnetron elements of a microwave receiver have been described. A magnetron-detector and a magnetron-oscillator are arranged with a common magnetic field, which is adjusted at a value close to optimum. The several controls for tuning the receiver may be combined to simultaneously adjust the operating parameters to a desired microwave length. The incoming signal currents and the local oscillator currents are made to react on each other through coupling between the tube electrodes. This coupling is substantially independent of the adjustments of the associated resonant lines. These adjustments would have a substantial effect on the coupling if the resonant lines were coupled at a point remote from the anodes.

I claim as my invention:

1. A microwave receiver comprising a circuit responsive to incoming microwave currents, a magnetron detector including anode electrodes, means including connections from said circuit to said anode electrodes for impressing said signal currents on said magnetron, a second magnetron including anode electrodes, a second circuit resonant to a frequency differing from said microwave currents connected to said second magnetron anode electrodes, means including a capacity for mutually coupling the electrodes of said magnetrons, means for creating a common magnetic field for said magnetrons, and means responsive to currents of a frequency equal to said different frequency effectively coupled to one of said` circuits.

2. A microwave receiver comprising means responsive to incoming microwave currents, a magnetron detector having anode electrodes, means connecting said anodes to said responsive means, a magnetron-oscillator having anode electrodes, means connected to said oscillator anode electrodes responsive to a frequency different from said microwave frequency, means including a capacity for mutually coupling said oscillator anode electrodes and said detector anode electrodes, means for creating a common magnetic field for said magnetrons, means for adjusting the strength of said field, and means responsive to currents of a frequency equal to said difference frequency.

3. A microwave receiver comprising a resonant line, means for adjusting the effective length of said line, a magnetron including anode electrodes, means connecting said line to said anode electrodes, a second magnetron including anode electrodes,a second resonant line, means connecting said second line to the anode electrodes of said secon-d magnetron, means for adjusting the effective length of said second resonant line to'a length slightly different from said rst line, means for mutually coupling the anode electrodes of said magnetrons, means for creating a common magnetic field for said magnetrons, means connected to said magnetic field creating means for adjusting the strength of said field, and means responsive to currents of an effective Wave length inversely proportional to said difference in effective lengths connected to one of said resonant lines.

4. In a device of the character of claim 3 a cathode common to the anodes of each of said magnetrons.

5. In a device of the character of claim 3 a common means for .adjusting the effective length of said first line, said magnetic field and the operating parameters of `said first-mentioned magnetron in substantial accordance with the formulas -1300y V=10 `2d and L=flk\ Where- Hzmagnetic field in gauss, k=wave length in centimeters, d=diameter in centimeters, V=voltage of .anode With respect to cath- 0de, L=length in centimeters, n=integral number of half Wave lengths and lc=a fraction of a half wave length.

6. In a device of the character of claim 3 a common means for adjusting the effective length of said second line, said magnetic eld and the operating parameters of said second-mentioned magnetron in substantial accordance with the formulas (i 2 =1300iV=12d and L=n `f2 Where H=magnetic eld in gauss, k=wave length in centimeters, d=diameter in centimeters, Vzvoltage of yanode with respect to cathode, L=1ength in centimeters, n=integra1 number of half Wave lengths and 1c=a fraction of a half Wave length.

'7. In a device of the character of claim 3 a common means for adjusting the effective length of said rst line, said magnetic field, the operating parameters of said first-mentioned magnetron, the effective length of said second line, said magnetic field and the operating parameters of said second-mentioned magnetron in substantial accordance With the formulas Where H=magnetic field in gauss, k=wave length in centimeters, d=diameter in centimeters, V=voltage of anode with respect to cathode, L=length in centimeters, n=integral numn k and ber of half Wave lengths and k--a fraction of a half Wave length.

8. A magnetron device having anode and cathode electrodes, a resonant line connected to said electrodes, means connected to said resonant line for adjusting the eiective length of said line, means for creating a magnetic field, means connected to said last-mentioned means for varying the strength of said field, a source of anode voltage, means connected to said source for varying said voltage, and a common control connecting said length-adjustment means, said field adjusting Imeans and said voltage varying means whereby a common adjustment may be made to effect substantially optimum operating characteristics of said device.

9. A magnetron device having anode and cathode electrodes, a resonant line connected to said electrodes, means connected to said resonant line for ,adjusting the effective length of said line, means for creating a magnetic eld, means connected to said last-mentioned means for varying the strength of said field, a source of anode voltage, means connected to said source for varying said Voltage, and a common control connecting said length-adjustment means, said field adjusting means and said voltage varying means whereby said magnetron device may be adjusted by said common control in accordance With the formulas length in centimeters, d=diameter in centimeters, V=voltage of anode with respect to cathode, L=length in centimeters, 1t=integral number of half Wave lengths and kza fraction of a half Wave length.

RENE A. BRADEN. 

